Paper surface sizing process and product utilizing cationic amylose derivatives

ABSTRACT

SIZING OF PAPER AND PAPERBOARD PRODUCTS WHICH COMPRISES APPLYING AN AQUEOUS DISPERSION OF A CATIONIC AMYLOSE DERIVATIVE TO AT LEAST ONE SURFACE OF A PREVOUSLY PREPARED CELLULOSIC WEB.

United States Patent 3,671,310 PAPER SURFACE SIZING PROCESS AND PRODUCT UTILIZING CATIONIC AMYLOSE DERIVATIVES Gerald H. Brown, Lebanon, and Emil D. Mazzarella, Mountainside, N.J., assignors to National Starch and Chemical Corporation, New York, N.Y. No Drawing. Filed May 7, 1968, Ser. No. 727,361 Int. Cl. D21h 1/34 US. Cl. 117-156 Claims ABSTRACT OF THE DISCLOSURE Sizing of paper and paperboard products which comprises applying an aqueous dispersion of a cationic amylose derivative to at least one surface of a previously prepared cellulosic web.

Paper and paperboard are often sized with various materials for the purpose of increasing their strength, their resistance to picking and scuffing, and their resistance to undue penetration of water, organic solvents, oils, inks and various types of aqueous solutions as well as for the purpose of improving their smoothness and optical characteristics. When sizing materials are applied to the surface of a finished web or sheet in order to cement the surface fibers to the body of the paper and to modify the sheet surface, the process is known as external or surface sizing; the latter process being quite distinct from an internal sizing process wherein sizing agents are admixed with the pulp slurry prior to its being converted to the form of a web.

Among the materials that have been utilized as surface sizing agents are included: conventional starches, polyvinyl alcohol, cellulosic derivatives, gelatin, animal glues, proteins, and various synthetic polymers, etc. Although all of these materials are effective under certain conditions, their use is nonetheless subjectto one or more limitations. Thus, for example, it is often necessary to utilize high concentration levels of such sizes in order to achieve the desired strength and holdout characteristics. Since it is known that the opacity and brightness of the base paper sheet decrease in proportion to the amount of size that is applied thereto, a direct result of the required use of such high concentration levels is a reduction in the optical properties of the treated paper. Furthermore, the use of such high concentration levels makes the sizing of specialty papers an economically unattractive proposition inasmuch as high cost, quality sizes, e.g. gelatin, animal glue and casein, are usually utilized for such purposes. In addition, certain prior art sizing agents must be used in conjunction with insolubilizing agents in order to impart satisfactory water resistance characteristics.

It is the object of this invention to provide improved surface sizing agents whose use results in the preparation of paper which is characterized by its improved strength, appearance, scuff resistance, printability and optical properties as well as by its reduced water and ink absorption. A further object of this invention involves the use of surface sizing agents which may be satisfactorily employed with all types of paper fiber. Various other objects and advantages of this invention will become apparent to the practitioner from the following detailed description.

We have now discovered that the use, as surface sizes, of cationic derivatives of amylose products has resulted in the preparation of paper and paperboard products which display a wide variety of improved properties. Thus, such sizes provide excellent surface strength and abrasion or scufi resistance properties. Moreover, they ice are capable of imparting improved water resistance and wet abrasion properties without the necessity of being combined with insolubilizing agents. Inasmuch as such sizes are capable of performing satisfactorily at lower addition levels, the decrease in opacity which generally accompanies the use of higher concentrations of sizing materials is avoided. In addition, these novel sizing agents form more continuous and uniform films on the surface of the paper or paperboard, thereby providing improved holdout characteristics which are evidenced, for example, by a greater resistance to ink absorption and by improved coating holdout. And, of great importance is the fact that such surface sizes can be utilized at reduced concentration levels without sacrificing any of their improved performance characteristics.

It should be noted that the aforementioned improvements are not realized when amylose products which are either underivatized or substituted with non-cationic groups are utilized in a surface sizing operation. Thus, underivatized amylose products are entirely inapplicable for use as surface sizes due to their instability, as evidenced by rapid retrogradation and viscosity variations, and their poor adhesion to cellulosic substrates. Noncationic amylose derivatives also fall far short of the level of effectiveness exhibited by their cationic counterparts.

It is well known that starch is generally composed of two fractions, one a linear fraction known as amylose, and the other a branched fraction known as amylopectin. Each starch type, e.g. corn, potato, tapioca, etc., contains these two fractions in a specific ratio characteristic of that particular starch with typical amylose concentrations ranging from about 18 to 30%, by weight. Methods for separating starch into these components are known. Additionally, some starches have been genetically developed which are characterized by a large preponderance of the one fraction over the other.

Thus, when we use the term amylose or amylose product" for the purposes of this invention, we refer to the amylose resulting from the fractionation of whole starch into its respective amylose and amylopectin components; or, to whole, high amylose starch which is composed of at least about 50%, by weight, of amylose; or, to mixtures of high amylose starches or amylose fractions with conventional, low amylose starches wherein the total amylose content of the resulting mixture is at least about 50%, by weight. In each instance, the amylose or high amylose starch may be further treated as with heat and/or acids or with oxidizing agents so as to form socalled dextrins, thin boiling or oxidized products; the latter products being especially preferred in sizing operations where starch solutions containing higher solids contents are required. In addition, the amylose base may be derivatized as by means of an esterification procedure which would thus yield amylose esters such, for example, as the acetate, sulphate and phosphate esters; or by means of an etherification reaction which would thus yield amylose ethers such, for example, as the hydroxyethyl and hydroxypropyl ethers. It should be noted that the latter modifications may be conducted either before or after the cationic derivatization of the selected amylose product.

As previously noted, the essence of our invention comprises the use, as surface sizing agents, of amylose products which contain cationic substituent groups, i.e. chemical groups which serve to introduce a positive electric charge into the starch molecule. The presence of the latter cationic groups aids in stabilizing the amylose product as well as in promoting the adhesion of the size to the cellulosic fibers.

Such cationic amylose derivatives may be made, for example, by reacting an amylose product, ordinarily through an etherification or esterification reaction, with any reagent which will introduce a cationic group containing nitrogen, sulfur or phosphorus therein. Examples of such groups are the amine (primary, secondary, tertiary or quaternary), sulfonium and phosphonium groups. The preferred cationic amylose derivative is the tertiary amino alkyl ether resulting from the reaction of an amylose product, under alkaline conditions, with a dialkyl amino alkyl epoxide or dialkyl amino alkyl halide, or the corresponding compounds containing aryl groups in addition to the alkyl groups. The general method for the preparation of such products is described in US. Pat. 2,813,093, issued Nov. 12, 1957.

Although we prefer the tertiary amino alkyl ethers of amylose, the primary and secondary amine derivatives as well as the corresponding amylose esters may also be used. Thus, beside the reagents already named, one may react an amylose product with amino alkyl anhydrides, alkyl imines, amino alkyl epoxides, amino alkyl halides, alkyl amino alkyl epoxides or halides, amino alkyl sulfates, and the corresponding compounds containing aryl in addition to alkyl groups. Furthermore, one may also employ tertiary amino alkyl ethers of amylose which also contain either hydroxyalkyl, e.g. hydroxyethyl, hydroxypropyl, etc., groups or ester, e.g. acetate, sulfate, phosphate, etc., groups. Such difunctional derivatives may be prepared by subjecting an amylose product to a hydroxyalkylation or esterification reaction along with the requisite aminoalkylation reaction in a procedure whereby the two reactions may be conducted simultaneously or in any desired order.

As pointed out previously, the sulfonium and phosphonium derivatives are also cationic in property and therefore suitable for the purposes of this invention. The general preparation of sulfonium derivatives is described in US. Pat. 2,989,520, issued June 20, 1961, and involves essentially the reaction of starch, in an aqueous alkaline medium, with a beta-halogeno alkyl sulfonium salt, vinyl sulfonium salt or epoxy alkyl sulfonium salt. The general preparation of phosphonium derivatives is described in US. Pat. 3,077,469, issued Feb. 12, 1963, and involves essentially the reaction of starch, in an aqueous alkaline medium, with a beta-halogeno alkyl phosphonium salt. Other suitable derivatives will be apparent to the practitioner, since our invention may employ any amylose derives which have been rendered cationic by the introduction of an electrically positively charged moiety into the amylose molecule.

Returning now to the class of cationic amylose derivatives containing amine groups, the following are some representative reagents which may be reacted with an amylose product to result in such derivatives: ethylene imine; propylene imine; isatoic anhydride; quinolinie anhydride; beta-diethyl amino ethyl chloride; beta-dimethyl amino isopropyl chloride; beta-dimethyl amino ethyl chloride; 3-diethyl amino 1,2-epoxypropane; 3-dibutyl amino 1,2-epoxypropane; 2-bromo-5-diethyl amino pentane hydrobromide; N-(2,3-epoxypropyl)piperidine; and, N,N-(2,3-epoxypropyl)methyl aniline. The various halides, e.g. chloro-, bromo-, etc., can be used interchangeably. 'In the above reagents, where the free amines have been indicated, e.g. beta-diethyl amino ethyl chloride, one can also use the hydrochloride or other salts of these reagents, e.g. beta-diethyl amino ethyl chloride hydrochloride. In fact, it is ordinarily preferred to use the salts since these tend to be less toxic and more easily handled. It should be noted that beside the alkyl, aryl and aralkyl types, the reagents may also include those containing cyclic groups.

It should also be mentioned that the amylose-amine products may be subsequently treated by known methods so as to result in the quaternary ammonium salt, or, such a quaternary ammonium salt may be made directly from an amylose product by treating it with the reaction product of an epihalohydrin and a tertiary amine or tertiary amine salt. In either case, the resulting amylose derivative is cationic in nature and is suitable for use in the novel process of this invention.

With regard to the degree of substitution which is required in the cationic amylose derivatives suitable for use as surface sizing agents in our process, we have found it advisable to react the selected amylose product with sufiicient cationic reagent in order that the resulting cationic amylose derivatives exhibit a degree of substitution (D.S.), i.e. the number of cationic substituent groups per anhydroglucose unit of the amylose molecule, ranging from about 0.01 to 0.20, and preferably from 0.02 to 0.10; the latter derivatives thus being capable of providing the previously discussed improvements in strength and appearance, etc.

The surface sizing agents of this invention may, of course, be successfully utilized for the sizing of paper and paperboard products, including sheet-like masses and molded products, prepared from all types of both cellulosic and combinations of cellulosic with non-cellulosic fibers. The cellulosic fibers which may be used include bleached and unbleached sulfate (kraft), bleached and unbleached sulfite, bleached and unbleached soda, neutral sulfite, semLchemical, chemi-groundwood, groundwood, and any combination of these fibers. The latter designations refer to wood pulp fibers which have been prepared by means of a variety of processes which are known in the pulp and paper industry. In addition, synthetic fibers of the viscose rayon or regenerated cellulose type as well as of the chemically synthesized type can also be used. For purposes of convenience, the sheets or webs derived from the latter materials will all, hereinafter, be referred to as cellulosic webs or sheets.

All types of pigments, dyes, rosin and fillers may be present in the paper which is to be sized with our sizing agents. Such materials include clay, talc, titanium dioxide, calcium carbonate and diatomaceous earths. Other materials such, for example, as conventional starch and resin sizing agents, pigments, dyes and lubricants, etc. can also be used in conjunction with our novel sizing agents.

The actual use of our surface sizing agents involves dispersing the cationic amylose derivative in water, the total solids contents of the resulting dispersion usually ranging from about 2 to 20%, by weight, and then applying the dispersion to a previously prepared paper or paperboard substrate by means of any conventional surface sizing technique. Included among the latter techniques are size press, tub, gate roll applicators and calender stack sizing procedures. Thus, for example, in a size press technique, surface sizing is accomplished by passing the web of paper between a pair of press rolls wherein the lower roll of the pair is rotating in a bath of the sizing dispersion. The surface of this roll picks up the size and deposits it on the lower surface of the web. If desired, sizing may also be applied to the upper surface of the web by spraying it into the nip formed between the web and the upper roll, or by spraying it against the surface of the upper roll and allowing it to accumulate on the upper surface of the web as it enters the press. The sized Webs are then dried by means of any conventional drying operation.

With respect to proportions, our sizing agents may be employed in amounts ranging from about 0.25 to 15.0% of the dry weight of the pulp in the finished web or sheet. Within this range, the precise amount which is used will, of course, depend for the most part upon the type of pulp which is being utilized, the specific operating conditions, as well as the particular end use for which the paper is destined.

The following examples will further ilustrate the embodiment of this invention. In these examples all parts given are by weight unless otherwise noted.

EXAMPLE I t This example illustrates the use of a typical surface sizing agent of this invention as well as the improved properties exhibited by paper that had been sized therewith.

The cationic sizing agent utilized in this example was a diethyl amino ethyl ether of a high amylose corn starch containing 70%, by weight, of amylose and having a D8. of 0.05. This tertiary amine derivative was prepared by the reaction of the amylose base with beta-diethyl amino ethyl chloride hydrochloride according to the general procedure described in Example I of U.S. Pat. 2,813,093.

\A sizing dispersion comprising 7 parts of the above described cationic amylose derivative in 93 parts of water was prepared and applied, by means of a typical size press procedure, onto a paper sheet which has been prepared from bleached sulfite pulp in accordance with the standards of the Technical Association of the Pulp and Paper Industry ,(TAPPI). The resulting paper sheet, which had thus been sized, surface sized with 3% of the sizing agent, as based on the dry weight of the pulp therein, was then dried at a temperature of 105 C. for a period of 10 minutes.

Using the test procedures described below, we then compared the properties of the thus sized paper sheet with those of a sheet of the identical paper which had not, however, been surface sized as well as with the properties of an identical paper sheet which, in this case, had been surface sized with 3%, by weight, of a tertiary amine sizing agent having a D8. of 0.05 which resulted from the reaction of a conventional, i.e. low amylose, corn starch with beta-diethyl amino ethyl chloride hydrochloride.

Wax Pick Test.This procedure measures the resistance of a coated paper surface to picking by means of TAPPI Test T 459m-48. In this procedure, melted waxes of graded adhesive strengths, each wax being numbered, were adhered to both the wire, i.e. bottom, and felt, i.e. top, surfaces of the respective paper sheets, allowed to cool and harden, and were then pulled from the sheet. The wax pick value assigned to any given paper surface is the value of the highest numbered wax which did not disrupt the paper surface. A paper surface having a high pick value thus possesses a superior surface strength than a paper surface having a lower pick value.

K & N Ink Holdout Test.This test measures the resistance of a paper surface to ink penetration. In this procedure, a standard, oil-based ink was wiped onto the surface of the respective paper sheets, allowed to remam in contact therewith for a period of 2 minutes, and then completely removed from their surfaces. TAPPI brightness readings were taken on the ink treated sample and compared with the brightness values exhibited by the untreated paper sheets. The K & N Holdout value was then determined by means of the following formula:

Percent K & N Holdont=l initial brightness-brightness of treated sheet 100 X initial brightness The following table presents the results which were obtained upon submitting the various paper sheets to the above described test procedures.

Wax pick test K & N ink holdout Sizing agent Wire Felt (percent) Cationic amylose derivative 16 11 55 Cationic corn starch 14 48 Control 12 7 42 with conventional, i.e. low amylose, cationic corn starches.

In addition, it should be noted that when an attempt was made to subject paper sheets which had been surface sized with an underivated high amylose corn starch containing 70%, by weight, of amylose to the above described test procedures, it was not possible to obtain any quantitative data in view of the inherent instability of this amylose product and the resulting difficulties encountered in attempting to apply it to the base paper sheet.

EXAMPLE II This example further illustrates the improved properties exhibited by paper sheets which have been surface sized with our cationic amylose derivatives.

Utilizing the general procedures set forth in Example I, hereinabove, paper sheets were prepared which were sized, respectively, with the cationic amylose derivative described in Example I and with various conventional sizing agents. Performance characteristics of the resulting paper sheets were then determined by submitting the sheets to one or more of the following test procedures:

Wax Pick Test.as described in Example I.

K & N Ink Holdout Test.-as described in Example I.

Opacity Test.The opacity of the paper sheet specimens was determined according to TAPPI test method T 425m-60. This test procedure determines opacity by means of a variety of reflectance measurements off the test sample; a value of being indicative of total opacity.

Cobb Size Water Absorption Test.This test measures the water resistance of a coated surface. Thus, an openended cylinder having an area of 100 square centimeters was placed on a surface of the sized paper sheet and filled with water to a depth of one centimeter. The water was allowed to remain in contact with the paper sheet for a period of 10 minutes. Thereafter, the surface of the sheet was wiped dry and a determination made as to the increase in weight exhibited by the exposed area. Needless to say, lower percentage weight increases will be observed in sheets which exhibit greater resistance to water.

1 A calendar stack sizing technique was utilized in applying the sizing agent to a bleached paperboard.

The results presented above clearly indicate the increased resistance to water and ink absorbancy provided by paper sheets which have been sized with our cationic amylose sizing agents as contrasted with sheets which have been sized with a conventional surface sizing agent.

Percent sizing Wax agent, pick by wt. of test, Opac- (B) Sizing agent dry pul felt my Cationic amylose derivative of Ex. I 3.0 13-14 95. 0 o 4. 5 14-16 94. 5 A corn starch which had been enzyme converted to a viscosity known in the trade as 42 sec. Dudley at 13% solids 6.0 11 94. 0

Thus, it is of real significance that the surface pick-up of our sizing agents may be reduced by as much as 50%, as compared with that of a conventional sizing agent, without sacrificing any of the surface strength characteristics of the treated paper. Such reductions in the concentration of the sizing agent are even more desirable in view of the opacity increases that result therefrom.

The results summarized above further indicate the unique properties of our sizing agents, as compared with conventional sizing agents, inasmuch as they show that it is possible to effect a 50% reduction in the surface pickup of the sizing agent without sacrificing the surface strength characteristics of the sized paper sheets.

Percent sizing agent, Wax pick test by wt. of (D) Sizing agent dry pulp Wire Felt Cationic amylose derivative of Ex. I 4. 18 16 An acetate ester of a high amylose corn starch containing 70%, by weight, of amylose and being substituted with 4.5%, by weight, of acetyl groups 5.1 16 14 The results summarized above clearly indicate the necessity for the presence of cationic substituent groups on the amylose products in order to provide the desired improved surface sizing characteristics.

EXAMPLE III This example illustrates the use, as surface sizing agents, of amylose products which have been substituted, respectively, with a variety of different cationic groups.

The following cationic amylose derivatives were each utilized to size paper sheets according to the procedure set forth in Example I, hereinabove. The resulting paper sheets were then subjected to the Wax Pick and Opacity test procedures in order to determine their perform ance characteristics.

(1) A sulfonium ether of a high amylose corn starch containing 70%, by weight, of amylose and having a D8. of 0.06; the sulfonium ether having been prepared according to the general procedure set forth in U.S. Pat. 2,989,- 520.

(2) A phosphonium ether of a high amylose corn starch containing 70%, by weight, of amylose and having a D8. of 0.08; the phosphonium ether having been prepared according to the general procedure set forth in U.S. Pat. 3,077,469.

(3) A quaternary ammonium ether of a high amylose corn starch containing 70%, by weight, of amylose and having a D.S. of 1.2; the quaternary ammonium ether having been prepared according to the general procedure set forth in U.S. Pat. 2,876,217.

The results summarized above clearly indicate the applicability of this invention of a wide variety of cationic amylose derivatives.

Summarizing, it is thus seen that this invention provides a novel process for the improved surface sizing of paper and paperboard products.

Variations may be made in proportions, procedures and materials without departing from the scope of this invention which is defined by the following claims.

We claim:

1. A method of sizing a previously prepared cellulosic web which comprises applying, to at least one surface of said cellulosic web, an aqueous dispersion of a cationic derivative of an amylose product containing at least about 50%, by weight, of amylose, and thereafter drying the thus treated cellulosic web.

2. The method of claim 1, wherein said cationic deriva tive is selected from the group consisting of ethers and esters containing substituent groups selected from the class consisting of primary, secondary, tertiary and quaternary amine groups, sulfonium groups and phosphonium groups.

3. The method of cl'aim 1, wherein said cationic derivative contains from about 0.01 to 0.20 of cationic substituelnt groups per anhydroglucose unit of the amylose molecu e.

4. The method of claim 1, wherein the cationic derivative is applied to the surface of said cellulosic web in a concentration of from about 0.25 to 15.0%, the latter concentration being based on the dry weight of pulp in said web.

5. The method of claim 1, wherein said cationic deriva tive is the tertiary amino alkyl ether of an amylose product.

6. A paper product coated on at least one surface thereof with a sizing agent comprising the dried residue of an aqueous dispersion of a cationic derivative of an amylose product containing at least about 50%, by weight, of amylose.

7. The paper product of claim 6, wherein said cationic derivative is selected from the group consisting of ethers and esters containing substituent groups selected from the class consisting of primary, secondary, tertiary and quaternary amine groups, sulfonium groups and phosphonium groups.

8. The paper product of claim 6, wherein said cationic derivative contains from about 0.01 to 0.20 of cationic substituent groups per anhydroglucose unit of the amylose molecule.

9. The paper product of claim 6, wherein the cationic derivative is present on the surface of said paper product in a concentration of from about 0.25 to 15.0%, the latter concentration being based on the dry weight of pulp in said paper product.

10. The paper product of claim 6, wherein said cationic derivative is the tertiary amino alkyl ether of an amylose product.

References Cited UNITED STATES PATENTS 2,813,093 11/1957 Caldwell et al. 260-233.3 2,876,217 3/ 1959 Paschall 260 -233.3 2,989,520 6/ 1961 Rutenberg et al. 117139.5 X 3,052,561 9/1962 Kronfeld 117-156 X 3,077,469 2/1963 Aszalos 117-139.5 X 3,269,855 8/ 1966 Moes et al 117156 X 3,314,810 4/1967 Young 117156 X 3,318,715 5/1967 Tetenbaum 117156 X 3,329,523 7/1967 Best et al 117156 X 3,387,998 6/1968 Powers 117-156 WILLIAM D. MARTIN, Primary Examiner M. R. LUSIGNAN, Assistant Examiner U.S. Cl. X.R. 

